In an uplink (a direction from a user equipment to a network), when no dedicated channels (DCHs) and no corresponding dedicated physical data channels (DPDCHs) are configured, all data is transmitted on an enhanced dedicated channel (E-DCH) which is mapped to an enhanced dedicated physical data channel (E-DPDCH). Control signaling associated with the E-DCH is transmitted on an enhanced dedicated physical control channel (E-DPCCH). The E-DPDCH and E-DPCCH can be discontinuous and are transmitted only when there is data to be transmitted and the transmission has been granted by the network. In the uplink, in addition to the E-DPDCH and E-DPCCH, a continuous dedicated physical control channel (DPCCH) and possibly a continuous or discontinuous dedicated physical control channel (e.g., an uplink high speed dedicated physical control channel, HS-DPCCH) for an HS-DSCH (high speed downlink shared channel) are transmitted.
A packet service session contains one or several packet calls depending on the application as described in ETSI standard, TR 101 112, UMTS 30.03 “Selection procedures for the choice of radio transmission technologies of the LMTS”, version 3.2.0. The packet service session can be considered as an NRT (non-real time) radio access bearer duration and the packet call as an active period of packet data transmission. During the packet call several packets may be generated, which means that the packet call constitutes a bursty sequence of packets. The burstiness is a characteristic feature of the packet transmission.
The arrival of session set-ups to the network can be modeled as a Poisson process. Reading time starts when the last packet of the packet call is completely received by the user and ends when the user makes a request for the next packet call. The E-DCH transmission in the uplink is discontinuous during a reading time, such that during most of the reading time there is no E-DCH transmission. Note, that depending on the packet arrival intervals (among other things), there could be gaps in the E-DCH ) transmission during a packet call but the E-DCH transmission might also be continuous during the packet call. Thus, there can be some inactivity on the E-DCH also during a packet call.
In a UL direction from a user equipment (UE) to a network, also a signal on a high speed dedicated physical control channel (HS-DPCCH) can be transmitted. The HS-DPCCH signal typically carries 2 slots with channel quality indicator (CQI) reporting information and 1 slot with ACK/NACK information for the HSDPA. CQI transmission is typically periodic and normally independent of the HS-DSCH transmission activity. CQI reporting period can be controlled by a radio network controller (RNC) with possible values of 0, 2, 4, 8, 10, 20, 40, 80, and 160 ms. ACK/NACK is transmitted only as a response to a packet transmission on the HS-DSCH, which (similar to the E-DCH) is transmitted only when there is data to be transmitted and which depends on the reading time and packet arrival times during the packet call.
For the E-DCH transmission, a grant is needed: a non-scheduled grant for non-scheduled MAC-d (MAC stands for medium access control) flows and a serving grant (and allowed active hybrid automatic repeat request (HARQ) process) for a scheduled transmission. In the case of the scheduled MAC-d flows, a Node B controls when a user equipment (UE) is allowed to send and thus Node B knows when the UE may send data. For the non-scheduled MAC-d flows, the network can allow a maximum number of bits that can be included in a MAC-e PDU (protocol data unit) for the given MAC-d flows. In case of 2ms E-DCH TTI (transmission timing interval), each non-scheduled grant is applicable for a specific set of HARQ processes indicated by an RRC (radio resource control), and RRC can also restrict the set of HARQ processes for which scheduled grants are applicable. Also there must be a sufficient transmit power available in the UE to transmit the intended number of bits with the power level needed for intended reliability of the transmission, except for a minimum set (defined by the network), which defines a number of bits that can be transmitted on the E-DCH in the TTI also when there is not enough transmit power to maintain the intended reliability. (This minimum set for the E-DCH may only exist if there is no DCH configured for the connection.)
The UL DPCCH carries control information generated at layer 1 (physical layer). The layer 1 control information consists of, e.g., known pilot bits to support channel estimation for coherent detection, transmit power control (TPC) for DL DPCH (dedicated physical channel), optional feedback information (FBI) and optional transport format combination indicator (TFCI). Typically, the UL DPCCH is continuously transmitted (even if there is no data to be transmitted for certain time periods), and there is one UL DPCCH for each radio link. The continuous transmission is not a problem with circuit switched services, which are typically sent continuously. However, for bursty packet services, continuous DPCCH transmission causes a significant overhead.
The uplink capacity can be increased by decreasing a control overhead. One possibility for decreasing the control overhead is UL DPCCH gating (or discontinuous transmission), i.e., not transmitting signals on the DPCCH all the time.
Rationale for using gating includes (but is not limited to):                providing user equipment (UE) power savings and longer battery life;        providing interference reduction; and        providing higher capacity.        
There is a fast closed loop power control for all uplink signals to combat against the power imbalance between different user signals and fast fading. The Node B, e.g., estimates continuously a signal-to-interference ratio (SIR) of the DPCCH transmitted by the UE and compares an estimate to a target value, and transmits transmit power control (TPC) commands in a downlink to the UE to increase or decrease the transmit power level. With the power control, the signals from different UEs can be received with the required quality in changing conditions.
During the uplink transmission gap the UL power control cannot operate as normally because Node B cannot estimate the received signal quality to determine the proper TPC command (the SIR would be extremely low, and normally generated TPC commands would tell the UE to increase the UL transmit power). Therefore the transmission power to be used after the gap needs to be estimated or predefined. Due to a user movement or a change in propagation conditions (fading) it is likely that in case of a long transmission gap that the power used prior the gap is not sufficient to ensure a proper communication leading to increased usage of the HARQ or too excessive thus increasing a UL noise making the UL power control and scheduling of UL capacity (e.g., in case of a high speed uplink packet access, HSUPA) more difficult.